Abstract P348: Perfusion Collateral Index vs. Hypoperfusion Intensity Ratio in Assessment of Angiographic Collateral Scores in Patients With Acute Ischemic Stroke

Background and Purpose: In acute ischemic stroke (AIS), perfusion imaging, while not directly visualizing collateral vessels, can provide important insight into collateral robustness, indexed by perfusion lesion volume and by perfusion lesion heterogeneity. Two proposed perfusion lesion heterogeneity measures indexing collateral status are the Perfusion Collateral Index (PCI) and Hypoperfusion Intensity Ratio (HIR), but their accuracy compared with direct collateral assessment on DSA has been incompletely characterized. Methods: Consecutive AIS patients with anterior circulation large vessel occlusion who underwent pre-endovascular thrombectomy MRI perfusion imaging were included. MRI measures analyzed were: 1) Perfusion Collateral Index ( PCI) - the volume of moderately hypoperfused tissue (arterial tissue delay time between 2 and 6 seconds: ATD 2-6sec ) multiplied by its corresponding relative cerebral blood volume using Olea software; 2) Hypoperfusion Intensity Ratio (HIR) ratio of moderate TMax >6 s lesion volume versus severe Tmax >10 s lesion volume with the RAPID software program. DSA collateral scores were evaluated by ASITN grading and dichotomized to inadequate (ASTIN <2) vs. adequate (ASTIN ≥3). Results: Among 48 patients meeting entry criteria, age (mean ± SD) was 70 (± 15.2), 54% were female, and NIHSS (median, IQR) was 15 (10-19). For HIR, there was no significant difference in score values in patients with adequate vs inadequate collaterals: 0.35 ± 0.20 vs 0.39 ± 0.25, p=0.68. ROC analysis using previously described cut-off of 0.4 resulted in an AUC of 0.52 and sensitivity/specificity of 71% / 33%. For PCI, score values were significantly higher in patients with adequate vs inadequate collaterals, 117 ± 61 vs. 57 ± 41, p=0.002. ROC analysis using previously described cut-off of 62 resulted in an AUC of 0.8 and sensitivity/specificity of 84% / 78%. Conclusion: Collateral status can be accurately assessed on perfusion MRI with the Perfusion Collateral Index, which outperformed the Hypoperfusion Intensity Ratio. MRI-PCI is an informative imaging biomarker of collateral status in patients with AIS.